Carbon nanotube/silica composites obtained by sol-gel and high-pressure techniques

The successful incorporation of functionalized single-walled carbon nanotubes (f-SWCNTs) into a silica matrix prepared by the sol-gel method is reported herein. SWCNTs produced through catalytic chemical-vapor deposition (CCVD) have been purified and functionalized with sulfuric, nitric and hydrochloric acids to ensure a good dispersion in an aqueous solution. The nanotube composites are prepared using three concentrations of f-SWCNTs (0.025, 0.050 and 0.075?wt%.) in a silica matrix, resulting in translucent monoliths after gelation. Dense, crack-free and hard compacts are obtained by high-pressure processing at 7.7?GPa and room temperature. Compared to the pure silica compact, compacts containing 0.025 and 0.050?wt% f-SWCNTs show an increased toughness of about 54% and 69%, respectively. The influence of f-SWCNTs on some microstructural aspects of the silica matrix has been studied using nitrogen adsorption/desorption isotherms. Raman spectroscopy has been applied to analyze the effect of the silica matrix and high-pressure compaction on the f-SWCNTs incorporated into the silica matrix. These measurements showed that f-SWCNTs remained in the silica matrix under pressure, suggesting an important interaction with the matrix.     

Collision Avoidance Based on Line-of-Sight Angle

This paper focuses on the problem of collision avoidance for Unmanned Aerial Vehicles (UAVs). The dynamics of the UAV are modeled as a Dubins vehicle flying at constant altitude. The angular velocity is used as control input in order to avert a possible collision with a single obstacle, while the speed is left as an extra degree of freedom to achieve some temporal requirements. The proposed control algorithm uses only the line-of-sight angle as feedback: in this sense, the main contribution of this paper is providing a solution to the collision avoidance problem that can be used in situations where it is not possible to measure data such as position and velocity of the obstacle. A theoretical analysis of the result is provided, followed by simulation results that validate the efficacy of the control strategy.     

Mechanism of regeneration of broken chemical bonds in the spatial structure of glasses and natural high-silica materials

It is shown that it is possible to restore partially the chemical bonds and spatial structure of high-silica natural rocks and glass broken by crushing and milling. The obtained materials (blocks, plates, lightweight articles, etc.) can be used in the building industry.     

Artemisia dracunculus L. essential oil phytochemical components trigger the activity of cellular antioxidant enzymes

Investigation of dietary biologically active phytochemicals is of interest due to the availability, low cost, and low rate of side effects of these substances. The main objective of this work was to investigate the influence of the essential oil (EO) extracted from the aerial parts of Artemisia dracunculus on the antioxidant capacity of cells as this plant is one of the most available and widely used as spice and in folk medicine. For this, BV-2 microglial wild type (WT) and acyl-CoA oxidase type 1 (ACOX1) deficient cells (Acox1^−/−) were used. Acox1^−/− cells were applied as the model of cellular oxidative damage. The main component of EO of A. dracunculus was estragole, which was reaching 84.9% in plants cultivated at high altitude Armenian landscape. IC₅₀ value of EO in 1,1-diphenyl-2-picrylhydrazyl assay was 94.2 µg/ml. Sub-cytotoxic concentration in the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test for both BV-2 WT and Acox1^−/− cell lines was 5.10⁻¹ µg/ml. Seventy-two-hours treatment with EO leads to the increased viability (up to 12% in WT and up to 14% -in BV-2 Acox1^−/−cells). The 48-hr treatment increased the ACOX1 activity up to 70% in WT cells. Catalase and superoxide dismutase activities of both cell lines increased following the 24–48-hr treatment. These results indicate that A. dracunculus EO can be considered as a potential protective agent useful in preventive medicine.     

Kunitz-Type Peptides from Sea Anemones Protect Neuronal Cells against Parkinson’s Disease Inductors via Inhibition of ROS Production and ATP-Induced P2X7 Receptor Activation

Parkinson’s disease (PD) is a socially significant disease, during the development of which oxidative stress and inflammation play a significant role. Here, we studied the neuroprotective effects of four Kunitz-type peptides from Heteractis crispa and Heteractis magnifica sea anemones against PD inductors. The peptide HCIQ1c9, which was obtained for the first time, inhibited trypsin less than other peptides due to unfavorable interactions of Arg17 with Lys43 in the enzyme. Its activity was reduced by up to 70% over the temperature range of 60–100 °C, while HCIQ2c1, HCIQ4c7, and HMIQ3c1 retained their conformation and stayed active up to 90–100 °C. All studied peptides inhibited paraquat- and rotenone-induced intracellular ROS formation, in particular NO, and scavenged free radicals outside the cells. The peptides did not modulate the TRPV1 channels but they affected the P2X7R, both of which are considered therapeutic targets in Parkinson’s disease. HMIQ3c1 and HCIQ4c7 almost completely inhibited the ATP-induced uptake of YO-PRO-1 dye in Neuro-2a cells through P2X7 ion channels and significantly reduced the stable calcium response in these cells. The complex formation of the peptides with the P2X7R extracellular domain was determined via SPR analysis. Thus, these peptides may be considered promising compounds to protect neuronal cells against PD inductors, which act as ROS production inhibitors and partially act as ATP-induced P2X7R activation inhibitors.     

ℒ 1 adaptive controller for tailless unstable aircraft in the presence of unknown actuator failures

This article considers application of ?₁ adaptive controller to multi-input multi-output open loop unstable unmanned military aircraft. The control is designed to accommodate and to be robust to actuator failures as well as to pitch break uncertainty, which is used to model uncertain aerodynamics. Results of using the ?₁ adaptive controller are compared with the conventional model reference adaptive control scheme to show improved transient command tracking as well as guaranteed time-delay margin.     

In-situ FTIR analyses of bentonite under high-pressure

The stability of bentonite is of particular interest for containment barriers in nuclear waste disposal facilities. However, very little is known about the stability of montmorillonite (the major component of bentonite) under high-pressure (HP) conditions. The objective of this work is to investigate the stability of montmorillonite under HP conditions, using a sample of bentonite in which the major component is a dioctahedral calcium montmorillonite. This montmorillonite was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), specific surface area (SA), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). HP experiments up to 7.7 GPa at room temperature (RT) were performed using toroidal chambers (TC). The samples were characterized by XRD after the HP processing. In-situ FTIR analyses were performed in the samples inside a diamond anvil cell (DAC) up to 8 GPa (dispersed in KBr) and up to 13 GPa (pure bentonite). In-situ FTIR measurements inside the DAC showed that montmorillonite was stable despite a reversible deformation in the Si–O bond and did not lose water up to 13 GPa. XRD analysis of the samples processed at 8 GPa at RT inside the TC showed no marked modification in the (001) reflections and b-parameter (060) reflections of montmorillonite induced by high pressure. The obtained results indicated that montmorillonite remained stable under high pressure conditions.     

Stable adaptation in the presence of input constraints

For a class of linear dynamical systems with unknown parameters a direct model reference adaptive control framework is developed that provides stable adaptation in the presence of input constraints. The proposed design methodology, termed “positive μ-modification”, has the ability to protect the control law from actuator position saturation. The reference system is adaptively modified to ensure global asymptotic tracking for open-loop stable systems. For unstable systems an estimate for the domain of attraction is derived based on the input saturation magnitude and system parameters. Simulation of a benchmark example verifies the theoretical statements.